#clojure – 2008-07-25

2008-07-25

03:12	meredydd	Chouser: A-ha.
03:12	meredydd	Chouser: I had no idea what you were talking about, until I grepped the API document for ":state"
03:13	meredydd	and realised that what I thought was part of the paragraph about factory methods was in fact a description of another option.
08:32	meredydd	Hey...does the Java interop work with Java var-arg methods?
08:33	rhickey	there are no real var-arg methods in Java, they take arrays and, for now, to call them you have to pass arrays
08:34	meredydd	I'm aware that they're arrays behind the scenes
08:34	meredydd	I take it there's no tag you can examine to see who is and who isn't a var-arg method?
08:36	rhickey	there is, the problem is that Java uses types to detect the difference between passing an array (to match the array arg) and passing a non-array (which Java will turn into an array auto-magically)
08:38	rhickey	so it's (String/format "%d%d%d" (to-array [1 2 3])) for now
08:55	Chouser	probably warrants a mention on the java-interop page
09:02	cemerick	an impl of defbean (now called genbean) that I'm mostly happy with is finally done, along with a generalized approach for integrating it (and other gen-and-save-class usage) into a build process; hopefully, I'll get to writing it up for the group later today
09:03	rhickey	cemerick: cool, is there something you still wish you had for that?
09:04	cemerick	rhickey: not much, aside from the ability to define method impls in a gen-class body
09:05	cemerick	I ended up ditching the proxy approach entirely because invoking the polymorphic "makeNew" function was way too cumbersome
09:07	cemerick	a small thing would be to have a verbose-gen-class (or whatever) var that would println where gen-and-save-class is trying to save bytecode
09:09	lisppaste8	rhickey pasted "group-by partition-by" at http://paste.lisp.org/display/64190
09:10	cemerick	rhickey: oh, right the rumored, forthcoming name munging in gen-class would be really helpful in general
09:19	rhickey	Chouser: I think partition-by is a better name for what you were trying to do
09:20	rhickey	the version I pasted call f once per item
09:30	Chouser	yeah, group-by sound enough like relation-speak that it's better working on sets or maps.
09:31	Chouser	ok, very clever use of "identical?" on a lazy seq
09:34	Chouser	f gets called one extra time on the first item of each partition, doesn't it? for fv?
09:35	rhickey	could be drop-while ... (rest s) I guess, to avoid that
09:36	Chouser	ah, yep.
09:37	lisppaste8	rhickey annotated #64190 with "partition-by with no redundant calls" at http://paste.lisp.org/display/64190#1
10:03	lisppaste8	blackdog pasted "no matching field?" at http://paste.lisp.org/display/64193
10:04	blackdog	hi can someone tell me why i get a no matching field exception
10:04	blackdog	please
10:05	rhickey	blackdog: Woot doesn't derive from anything that has an actionPerformed method. You can't add methods by just putting them in the Clojure side
10:05	blackdog	oh,
10:06	blackdog	ok, i thought gen- classes were much more general than proxy,
10:07	rhickey	blackdog: they are, but you still have to make sure your methods are in the Java class itself, either by deriving or using the :methods argument to gen-class
10:08	rhickey	Java class signatures are not dynamic
10:08	blackdog	is there any way then to create a new class with some methods totally in clojure?
10:09	blackdog	i'm trying to attach some handlers to a gui designer, and it's looking for an object with actionPerformed methods
10:10	rhickey	the gen-class system partitions class definition into 2 parts - the part Java requires be static, i.e. the signature, and everything I can make dynamic (the implementation)
10:10	rhickey	the gui designer is looking for an instance of java.awt.event.ActionListener, no?
10:11	blackdog	well. it
10:11	blackdog	it's a runtime lib (jformdesigner) that reads xml descript
10:11	blackdog	and then you simply say setTarget(handlerobject)
10:11	blackdog	so i'm trying to setup the handler object
10:11	blackdog	in clojure
10:12	blackdog	the handler object is a pojo
10:12	blackdog	with just the correct methods names
10:13	blackdog	so i don't have anythign to derive from, but maybe i should investigate further the runtime api
10:13	blackdog	it may have more,
10:13	rhickey	well, you can proxy ActionListener, gen-class ActionListener, or gen-class :methods ... actionPerformed ...
10:14	blackdog	ok, i'll go off and think about that, thanks rhickey
10:24	blackdog	rhickey, gen-class :methods allows one to define the static part then?
10:25	rhickey	blackdog: everything in the gen-class defines the static part, but the :methods are just signatures. The definition still goes in the Clojure code as you had it
10:26	blackdog	but does the :methods get around having to derive or implement something - sorry for my denseness
10:27	rhickey	right, :methods are in addition to anything you get by deriving
10:27	blackdog	ok good, so that should work for me then
10:28	blackdog	ha! lift-off
10:29	blackdog	thanks!
10:29	rhickey	sure
14:58	cemerick	ach! why doesn't Google Groups support at least 80-column text? :-/
14:59	cemerick	ach! why doesn't Google Groups support at least 80-column text? :-/
15:00	rhickey	cemerick: yeah, if you have something substantial, you can attach it
15:01	cemerick	rhickey: where? I don't see any way to attach a file to a post. Or, do you mean upload it to the files section of the group?
15:01	Chouser	you may need to post via email, and attach to your email
15:01	rhickey	what he said
15:02	cemerick	ah. I should have done that.
15:03	rhickey	cemerick: you can still
15:04	cemerick	Yeah, I suppose I'll repost. It'll create a new thread, though, yes?
15:04	rhickey	or you can follow up to your original message with a short note and the attached file
15:07	cemerick	ah, I'll delete the original and send an email
15:13	cemerick	much better
15:22	rhickey	cemerick: a couple of thoughts, using the current ns as a name is very troubling - I know that's on me to provide defs of qualified names
15:22	rhickey	as far as get/set, setProperty is a problem - while it would be familiar looking, it won't be familiar behaving, as it doesn't modify the object in place.
15:26	rhickey	anyone want to take a crack at gen-interface? should be really easy, learn a little bytecode gen?
15:30	cemerick	rhickey: using the current namespace for the method impls and classname certainly isn't "hygenic", but that's what the typical usage would be anyway
15:31	cemerick	I don't mind at all having a setProperty that returns a new Foo, rather than having mutable semantics. That might freak out some Java/.NET people, but that's better than having broken equals semantics.
15:31	Chouser	gen-interface would take a single class, no options, and do the minimal gen-class equivalent for it?
15:31	rhickey	Chouser: no, allow the definition of an interface from scratch, just signatures
15:31	Chouser	I was thinking I might poke at gen-class function name mangling if nobody beat me to it.
15:32	Chouser	ah.
15:34	rhickey	Chouser: if '.' prefix is too clever, what about '-' ?
15:35	rhickey	other genclassers please chime in
15:35	Chouser	I was thinking I'd do something lengthy (and internally configurable), and just provide a def-gen-method to match the same mangling.
15:36	cemerick	we're talking about mangling names so as to avoid the name clashes with referred namespaces?
15:36	rhickey	cemerick: yup
15:36	Chouser	at least that would could be done now safely, and allow any code written using it to be forward compatible with any more minimal mangle that might be chosen later.
15:36	Chouser	s/would//
15:37	cemerick	I'd definitely avoid '.' as a prefix. A '-' prefix would be a 99% solution, certainly.
15:37	rhickey	the problem with a mangle hidden by a special def is - how do you call/test it? It's still a normal function
15:37	Chouser	i'd be worried (defn -foo) looks a lot like (defn- foo)
15:39	Chouser	you might need to have "this" bound when you call it manually, right? there aren't any other special rules?
15:39	rhickey	maybe, but both are implementation details, editor coloring clears up pretty well
15:39	cemerick	I've always liked the python convention of a double-underscore shrug
15:39	rhickey	Chouser: yes this, no, they are regular fns
15:39	rhickey	cemerick: Lisp uses - instead --method would be ok too
15:39	Chouser	but you could test by creating an instace of the class and calling them as methods -- that would get "this" right, and follow any mangling.
15:40	Chouser	python uses double-underscore surround the name, which makes it hard to say aloud: __foo__
15:40	cemerick	rhickey: yeah, I was just replying to Chouser's concern about a prefixed '-' appearing too similar to defn-
15:40	Chouser	I guess "dash dash foo dash dash" is a bit better.
15:40	rhickey	as methods they are less powerful than fns, not first-class
15:40	rhickey	can't map etc
15:41	rhickey	Chouser: we have to stay off the end, already used for types
15:41	Chouser	ah, right. ok, so dump def-gen-method, and we'll just finish this mangling detail discussion right now. :-)
15:41	cemerick	Chouser: actually, "private" names in python usually have double-underscore only in front of the name -- that's what triggers name mangling
15:41	Chouser	cemerick: oh! ok.
15:42	Chouser	I'm fine with a -- prefix. shrug
15:42	Chouser	or a .. prefix, or #! or whatever. ;-)
15:43	cemerick	yeah, I really don't think it matters, outside of not using '.'. :-)
15:45	cemerick	actually, '-' sorts ahead of most other chars, which would be unfortunate for tools, etc.
15:46	rhickey	another potential issue with -- is it get munged to __, which is a name component I presume the Clojure implementation "owns"
15:46	Chouser	we don't really want anything starting with # since that triggers reader magic, right?
15:46	cemerick	pipes would work, and they sort after all other ascii chars; not so pretty, tho
15:46	rhickey	Chouser: right!
15:46	Chouser	* mean "global"
15:46	Chouser	% is already taken
15:47	rhickey	I'm reserving all other special chars
15:47	Chouser	@ and ~ are already taken pretty globally as well, right?
15:47	Chouser	oh. so it has to be -, ., or alphanumeric?
15:47	rhickey	this isn't worth a special character
15:48	Chouser	and since I think a prefix makes a lot of sense (compared to a postfix), it's really just alpha.
15:48	Chouser	-- is apparently dangerous, so either just "-" or something like "method-" or "gen-"
15:49	cemerick	well, these names aren't going to be accessed with any kind of regularity, right?
15:49	Chouser	the only other requirement being that it is very unlikely for a Java class to use in a normal method name.
15:49	cemerick	(by non-generated code, I mean)
15:49	rhickey	I'm not sure sorting first is bad, when looking at a ns dedicated to a class implementation, the methods will sort first
15:53	Chouser	any kind of prefix will have them sorted together. Having them first seems a little nicer than having a bunch of "method-*" between your "loo" and your "noo" functions.
15:53	rhickey	cemerick: right, the names might only rarely be used
15:54	Chouser	"-m-" prefix
15:54	cemerick	Chouser: +1
15:54	Chouser	that would sort first, stand out more than just "-", suggests a method without being verbose
15:55	Chouser	and if that gets mangled to "_m_" I think we've avoided better than 99.9% of Java method names.
15:56	rhickey	Chouser: the only conflict with - is if a class defined public foo and _foo, even then, one becomes _foo and the other __foo
15:57	rhickey	alpha prefixes dramatically reduce readability imo, - disappears, but m doesn't
15:58	Chouser	I agree - is technically sufficient, I'm just not convinced the difference between (defn- foo) and (defn -foo) is unmistakable.
15:58	Chouser	hm.
15:59	rhickey	in my editor defn- foo is all black and defn -foo is purple/blue
16:02	rhickey	ericthor: any thoughts if you are there? (enclojure might have more genclass than anyone)
16:07	rhickey	or we could use _, to remind us we're in Java-land
16:07	rhickey	(defn- foo (den _foo
16:08	rhickey	(defn- foo (defn _foo
16:17	Chouser	works for me, but either is fine.
16:18	rhickey	on an unrelated note: (derive java.util.Collection `aggregate) will work
16:19	rhickey	i.e. superimpose your own taxonomy on existing classes
16:40	mebaran151__	is there a good way to get an arbitrary hash for an arbitrary object that would ensure uniqueness on value: I'd like to use this string representation for a primary key functionality in an app i'm writing
16:42	Chouser	sounds like you want sha1 or md5
16:51	mebaran151__	for like a whole map though?
16:52	mebaran151__	like I'd like to be able to just take a random hashmap I created in clojure and run a function on it to return a string
16:52	mebaran151__	that would be unique over the values of that hash
16:52	mebaran151__	internally, that must be how clojure handles equality I would think
16:55	Chouser	whole maps have a hash value, but there's no guarantee they're unique -- when placed in a map or set a value comparison needs to be done to make sure you've really got the right item
16:55	Chouser	I think. That's normal for hashes, though.
16:56	Chouser	For equality you can use "identical?", but that'll give you false negatives. To be sure, I think the whole collection is compared.
16:58	mebaran151	yeah
16:58	Chouser	so if you want a guaranteed-unique hash, I think you'd have to use md5 or sha1 on the whole value.
16:59	mebaran151	it's a cool little project: trying to layer a fs db written in clojure
16:59	mebaran151	I might just go with my old idea of incrementing a string
16:59	Chouser	If the value is made up of just well-printable clojure objects, you could print to a string and run sha1 on it.
17:00	mebaran151	oh that's actually decent idea
17:00	mebaran151	yes
17:00	mebaran151	most of the objects will be well printable
17:00	mebaran151	I'm actually planning on internally bucketing the objects via their printed forms anyway
17:19	Chouser	woo! I've been stabbing in the dark, and finally hit my target. Now I just have to understand it...
17:20	rhickey	Chouser: what target?
17:20	Chouser	prepending a - on function names but not method names. ;-)
17:20	Chouser	It's taken me, what, an hour? It would have taken you 15 seconds.
17:21	Chouser	I'm trying to find where we discussed before which names you wanted mangled and which you wanted to leave alone.
17:21	rhickey	Chouser: ah, yeah, it's a bit thick in there
17:21	Chouser	heh. yeah. But I don't know a better way to learn it.
17:23	Chouser	ah, here it is. "the names manually given to genclass would remain unmunged? :factory, :state, etc?"
17:25	rhickey	I don't know, seems like the same arguments might apply - these names are dictated by outside requirements and could just as easily bang into clojure names - prefixed with _ they never would
17:25	rhickey	doing them all is probably way easier
17:26	Chouser	yeah. doing them all is (maybe?) done.
17:26	rhickey	cool!
17:26	Chouser	but not all the names are dictated -- init, state, etc.
17:26	rhickey	state is a field
17:27	Chouser	oh, "public". ok.
17:27	rhickey	I think it will be easiest for users too, to know the rule is clojure implementations of Java gen methods begin with _
17:28	rhickey	?
17:28	rhickey	public?
17:28	Chouser	I knew :state was a field, but I didn't realize it was public.
17:28	rhickey	yes, public and final, so no getter/setter
17:30	Chouser	well, maybe I'm completely missing something (seems likely), but my change is to replace genclass line 276: (. gen push (str "_" v))
17:30	Chouser	seems to work as expected.
17:31	Chouser	perhaps I need to test ctors, factories, etc.
17:32	rhickey	what about the lookup side?
17:33	rhickey	line 187?
17:35	blackdog	i'm trying to define a function defn as the body part of a macro
17:36	blackdog	and then using that as part of gen-and-load-class
17:36	blackdog	definition, but the function name has a _var appended
17:36	blackdog	[['wootActionPerformed [ActionEvent] Object]]
17:37	blackdog	Caused by: java.lang.ClassFormatError: Illegal field name "user/wootActionPerformed__var" in class igw/forms/Woot
17:37	blackdog	is that just a dumb thjing for me to try?
17:38	rhickey	blackdog: want to paste your macroexpansion?
17:38	blackdog	oh, i'll try, haven't really used that
17:38	blackdog	do i just stick macroexpand around the macro call?
17:39	rhickey	if you are having a macro problem, macroexpand is the first thing you should try, stick macroexpand around the quoted call
17:39	rhickey	(macroexpand '(my-macro x y z))
17:39	blackdog	ok
17:40	rhickey	if your macro expands into another macro, try macroexpand-1 first
17:42	blackdog	is there a pretty print for a macro?
17:42	blackdog	macroexpand?
17:42	rhickey	no pprint yet
17:42	blackdog	k
17:42	rhickey	emacs?
17:43	blackdog	no, i'm using jedit :(
17:44	lisppaste8	blackdog pasted "macroexpand" at http://paste.lisp.org/display/64223
17:45	blackdog	i don't see _var in the macroexpand
17:46	lisppaste8	blackdog pasted "stacktrace" at http://paste.lisp.org/display/64225
17:47	blackdog	the methods section in the macro itself is hard coded, would be replaced
17:48	rhickey	user/wootActionPerformed is not a valid method name, you have to generate an unqualified name
17:48	rhickey	the __var is added by the implementation of gen-class, but is not the problem
17:50	blackdog	in the macro it tries to do (in-ns ~kls) to set the ns before doing the defn of wootActionPerformed
17:50	rhickey	that's not going to work
17:50	blackdog	ok,
17:52	blackdog	because i;'m missing something fundamental or just that it's a daft thing to do?
17:54	rhickey	actually, I'm not sure what you are trying to do, but one trick is to fix your expansion by hand and see if it works before fixing the macro. Always start a macro with a by-hand implementation of the expansion that works, then tweak the macro until it expands to the same thing
17:55	blackdog	ok thanks for that,
17:55	rhickey	trying to get a macro and the expanded logic right at the same time is a recipe for pain
17:55	blackdog	ok
18:20	Chouser	rhickey: don't feel you need to walk me through this -- it'd probably be easier for you to just do it yourself. But if you want to answer my questions instead...
18:21	Chouser	If I mangle line 187 my tests fail.
18:22	Chouser	is it doing a lookup in the class there? I don't want to mangle that, of course.
18:48	rhickey	Chouser: I see - you are not changing the names of the static fields, just the var symbols - then you don't need line 187 changed
19:04	arohner	why can't I peek at a range?
19:04	arohner	user=> (peek (range 1 10))
19:04	arohner	(Peek (range 1 10))
19:04	arohner	java.lang.ClassCastException: clojure.lang.Range
19:04	arohner	java.lang.ClassCastException: clojure.lang.Range
19:04	arohner	at clojure.lang.RT.peek(RT.java:454)
19:04	arohner	at clojure.fns.clojure.peek__398.invoke(boot.clj:757)
19:04	arohner	at clojure.lang.AFn.applyToHelper(AFn.java:184)
19:06	arohner	user=> (peek '(1 2 3 4 5 6 7 8 9 10))
19:06	arohner	(peek '(1 2 3 4 5 6 7 8 9 10))
19:06	arohner	1
19:17	Chouser	peek is for lists, vectors, and queues. For generic seqs, you can just use first.
19:18	Chouser	(first (range 1 10))
19:18	arohner	ok
19:18	arohner	what is the difference between a seq and a list?
19:19	Chouser	oh, apparently peek is defined on IPersistentStack, which is implemented by list, vector and queue.
19:19	Chouser	arohner: that's a great question with a subtle answer.
19:20	arohner	yeah, I saw the IPersistentStack cast
19:20	arohner	that explained the stack trace, but didn't help me understand the issue :-)
19:20	Chouser	seq is an interface, specifically ISeq. Every ISeq provides "first" and "rest"
19:21	Chouser	every collection in clojure can viewed through a seq. For example: (seq {:a 1, :b 2})
19:22	Chouser	A list (PersistentList) is a concrete data structure, a singly-linked list. I happens to provide the ISeq interface itself directly, unlike most other collections.
19:23	Chouser	user=> (def x (list 1 2 3))
19:23	Chouser	user=> (identical? x (seq x))
19:23	Chouser	true
19:23	Chouser	user=> (def y {:a 1, :b 2})
19:23	Chouser	user=> (identical? y (seq y))
19:23	Chouser	false
19:24	arohner	ok, so the simple answer is that peek and pop are defined on things that have a stack interface
19:24	Chouser	right
19:28	arohner	thanks for the help
19:29	Chouser	np
19:51	mebaran151_	is it possible to join a lazy sequence to non-lazy sequence
19:53	mebaran151_	I want to do something like join at the head of list (1 2 3) to an infinite sequence of 4's for instance
19:54	mebaran151_	in the repl, lazy-cons produced the infinite sequence I didn't want it to do
19:55	Chouser	the repl will try to print all of a seq, lazy, infinite, or otherwise.
19:56	Chouser	(take 10 (lazy-cat (list 1 2 3 4) (repeatedly #(identity 4))))
19:57	Chouser	I'm not sure what the best way is to create an infinite seq of 4
19:57	Chouser	(take 10 (lazy-cat (list 1 2 3 4) (cycle [4])))
19:58	Chouser	ah!
19:58	Chouser	(take 10 (lazy-cat (list 1 2 3 4) (repeat 4)))
20:26	arohner	is there a library call that gives me all of the permutations of two lists?
20:27	Chouser	aren't permutations usually figured from a single list?
20:27	arohner	I want to pass two lists (range 1 10) (range 1 10) and get a list of tuples (1 1) (1 2) ... (10 9) (10 10)
20:27	Chouser	ah. for
20:27	arohner	maybe I'm using the wrong term
20:27	slava	the cartesian product of two lists?
20:27	mebaran151_	thanks Chousefr
20:28	Chouser	(for [x (range 10) y (range 10)] [x y])
20:28	arohner	ah, thanks
20:28	mebaran151_	hey Chouser, how can I tell if my recursion is occurring in the tail position
20:28	arohner	if you use (recur) it will be in the tail position, or you get an exception
20:28	Chouser	if the compiler lets you use (recur), then it's tail position.
20:29	mebaran151_	I'm trying to call recur inside an if conditional but clojure continually complaines
20:29	Chouser	what he said.
20:29	slava	why is recur in non-tail position prihibted?
20:30	mebaran151_	(def next-id (fn this
20:30	mebaran151_	([id] this (this id max))
20:30	mebaran151_	([id max] (loop [i id m max]
20:30	mebaran151_	(if (< (first i) (first m))
20:30	mebaran151_	(conj (incr (first i)) (rest id))
20:30	mebaran151_	(conj (base (first i))
20:30	mebaran151_	(recur (rest i) (rest m))))))))
20:30	mebaran151_	(sorry about the flood)
20:30	slava	mebaran151_: recr is not in tail position there because its result is passed to conj
20:30	mebaran151_	ah
20:30	slava	but i don't understand the limitation
20:30	arohner	because recur guarantees the stack size will not grow
20:30	mebaran151_	so how would I refactor this
20:31	slava	i'm not sure why you'd have recur at all
20:31	mebaran151_	well I'm recursively calling next-id
20:31	slava	so just call it explicitly i guess
20:31	mebaran151_	my id's are basically a seq of integers
20:31	mebaran151_	that can be of arbitrary length
20:31	arohner	mebaran, you probably need a loop position inside your ([id max]) case
20:32	mebaran151_	it's there
20:32	arohner	oh, right
20:32	mebaran151_	maybe there's a better way about it using reduce in some fancy way
20:33	arohner	you can self-call without the recur as well, you just aren't guaranteed the stack size won't grow
20:33	mebaran151_	I'm trying to basically do carry addition
20:33	slava	so is recur just an assertion basically that has no effect on the compiled code?
20:33	slava	how do you assert that a tail call to another function is a tail call?
20:33	arohner	no
20:34	arohner	the explanation I've heard is that the JVM doesn't have the opcodes to do a real tail call
20:34	arohner	recur only goes to designated places in your own function
20:34	arohner	a (loop), the top of the function, and a few other places
20:35	arohner	recur target is the term I'm looking for
20:35	slava	oh, right
20:35	slava	the JVM can't tail call, I forgot about that
20:36	slava	you can just do a goto within the current method
20:38	Chouser	slava: right, that's what recur does under the covers.
20:38	Chouser	which is why it has to be in tail position.
20:39	arohner	so I have a for loop that looks like
20:39	arohner	(for [x (range 1000)
20:40	Chouser	"on lisp" has a section which is where I learned how to move recursion to tail position.
20:40	arohner	(for [x (range 1000)
20:40	arohner	y (range 1000)]
20:40	arohner	(if foo (print "foo") nil))
20:40	arohner	when I evaluate that, the screen is filled with prints to nil
20:41	arohner	is there a way to not print all the nils?
20:41	Chouser	mebaran151_: instead of returning your accumulating value, pass it forward to the next recursive call, and finally return the whole thing at the end.
20:42	mebaran151_	I'm doing something similar with reduce right now
20:42	slava	that's something that the compiler should do though, not hte programmer
20:42	mebaran151_	I agree with slava here
20:42	Chouser	arohner: you're trying to program for side-effects, which will be fighting uphill in clojure. What are you trying to return?
20:43	slava	if the result of the non-tail-recursive call is the input to an associative operation, then its pretty easy to convert it to use an accumulator
20:43	mebaran151_	oh I'm trying to transform an array of ints as follows
20:43	slava	if its the input to cons, you convert it to an accumulator and reverse the list at the end
20:43	slava	pretty simple transformation to make
20:43	slava	the problem with doing it by hand is that its error-prone and you get a proliferation of auxilliary functions
20:44	mebaran151_	no int can be greater than the max value, and I'm incrementing from the left
20:44	arohner	ah, figured it out
20:44	arohner	:while
20:46	arohner	ah, I should be using :when and :while
20:46	arohner	I'm not really programming for side effects, I was just being lazy because I only cared about the last value
20:46	arohner	doing project euler stuff, so I just needed to see the last value and type it in
20:49	Chouser	slava: I'd be interested to see a patch to Clojure that does that.
20:52	Chouser	arohner: yeah, I just meant with "print". project euler is a great way to learn a new language.
21:03	mebaran151	my method didn't work: how would you transform my example?
21:09	Chouser	incr is the same as inc?
21:09	Chouser	oh, incr and base are your own?
21:10	mebaran151	yeah
21:10	mebaran151	it's a string incrementer of my own devising
21:11	mebaran151	kind of like Ruby's
21:16	Chouser	what does next-id return? I'm guessing a list?
21:17	rhickey	Chouser: a patch to Clojure that does what?
21:17	Chouser	does tail-call optimization at compile time.
21:17	rhickey	on a self-call?
21:18	Chouser	no, I kinda like the tail-position assertion of "recur". For non-tail-position and mutual-recursion cases.
21:19	Chouser	I think that's what slava was talking about, anyway.
21:19	rhickey	the JVM can't do mutual recursion TCO
21:20	Chouser	Yeah, I know. My understanding of what slava was saying is that the compiler could overcome the JVM's runtime weakness there.
21:20	rhickey	It can't
21:20	rhickey	I think he was just talking about not needing recur on self-call
21:21	Chouser	self-call in a non-tail position?
21:21	rhickey	self-call in tail position
21:21	Chouser	yeah, that's not interesting. :-)
21:22	rhickey	the reason that I don't is because of the expectation it creates among Scheme programmers
21:24	rhickey	this way it's easy to explain - there's no TCO, only recur is guaranteed non-stack-consuming
22:08	slava	Chouser: i was talking about an optimization that converts non-tail-calls into a tail call with an acculuator
22:08	slava	eg, (defun (fac x) (if (< x 3) x (* (fac (- x 1)) x)))
22:08	slava	this is not tail recursive
22:08	slava	but its easy to turn it into a tail recursive function
22:12	slava	people will expect a lisp compile to do this, so it will be surprising to many if clojure doens't
22:12	slava	they'll write fnctions that blow the stack without realizing it
22:21	Chouser	slava: are you working on a patch?
22:23	Chouser	Is it common for CL or Scheme to optimize non-tail calls? I haven't gotten that impression from the little reading I've done.
22:34	Chouser	can you guarantee all self-calls would be converted to tail-call? If not, that could cause even more surprising behavior.
22:37	albino	I doubt he's working on a patch, he has his own language to contend with
22:38	Chouser	ah
22:42	slava	Chouser: you can't convert all calls into tail calls of course
22:42	slava	its surprising inasmuch as any compiler optimization is
22:43	slava	but that's not an argument for non-optimizing compilers :)
22:44	Chouser	well if the difference between optimizing and not is a bit of speed, that's one thing. If it's the difference between blowing the stack and crashing or not, that kinda matters...
22:45	slava	does java crash when you exceed a fixed-size call stack allocation or does it grow the stack?
22:46	slava	i haven't done any java since 1.4 or so, i guess many things have changed
22:47	Chouser	if I do infinite recursion, it crashes
22:47	Chouser	((fn x [] (x)))
22:47	Chouser	boom
22:47	slava	because it fills up the heap?
22:48	albino	slava: how could one tell the difference?
22:49	slava	if the stack has a fixed size, then converting list operations to tail recursion with a list accumulator will be a win
22:49	slava	otherwise, not so much
22:50	slava	in both cases converting arithmetic to tail recursive form is a win because you'll run in O(1) space and not O(n)